JPH0251386A - Detector for generating torque of induction motor - Google Patents

Abstract

PURPOSE:To detect generating torque at an instant easily by detecting the instantaneous value of the generating torque of an induction motor by using the instantaneous values of the voltage and currents of the induction motor. CONSTITUTION:The input voltage of an induction motor 3 is detected by a voltage fundamental wave detector 4, and an instantaneous value or a signal proportional to the instantaneous value is output. The input currents of the induction motor 3 are detected by a current fundamental wave detector 5, and an instantaneous value or a signal proportional to the instantaneous value is output. A generating-torque arithmetic circuit 7 obtains phase difference between input voltage and input currents, acquires the input power of the induction motor from the phase difference, and divides the input power by rotational speed and obtains the instantaneous generating torque of the induction motor.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a device for detecting the instantaneous value of torque generated by an induction motor.

(Prior Art) Generally, the input current of an electric motor consists of a component proportional to the generated torque (torque component) and a component that generates a magnetic field (field component). In a DC shunt motor, power sources for these two current components exist independently in the armature circuit and the field circuit, so the two components can be detected individually and the generated torque can be easily detected.

On the other hand, in a squirrel cage induction motor, one AC power source is connected to the primary side, so these two components flow harmoniously together through the primary circuit. Among these, when vector control is applied to an induction motor, these two components are controlled independently, so even if these two components flow together as a primary current through the primary circuit, they can be detected individually. can. However, in squirrel cage induction motors that do not perform vector control, it is not easy to separate and detect these two components.

As a method for detecting the generated torque of a squirrel cage induction motor (hereinafter simply referred to as an induction motor) that does not perform vector control,
Conventionally, various methods have been proposed, and among them, there is a method in which input power is calculated from input voltage and input current, and this is divided by rotational speed to obtain generated torque. That is, in the equivalent circuit of the induction motor shown in Fig. 7, the input power P
1n can be calculated using the following formula.

P -3V' Icos θpp...(
1) n Here, ■ = Effective value of input phase voltage l Effective value of double input current θ1. This is the power factor angle seen at the heavy input end.

By substituting this human power P, the resistance r shown in the equivalent circuit of FIG. 7, the power loss Ploss at R, and the mechanical angular velocity ω into the following equation, the generated torque T can be obtained.゛ is required.

(Problem to be Solved by the Invention) The voltage and current in the above equation (1) are effective values, but when calculating them, if the frequency and amplitude are constant like a normal commercial power source, there is no equivalence problem. However, in variable voltage and variable frequency power supplies, the frequency and amplitude are not constant, so some measures are required.

For example, it is possible to obtain the effective voltage value by looking at the voltage waveform and averaging it over one period, and at the same time obtain the effective value of the current from the current waveform in the corresponding period. However, with this method, it is necessary to accurately determine the 0-cross point. Furthermore, until one cycle is determined, the value calculated in the previous cycle must be used, causing a delay in detection. This delay is particularly problematic when the frequency is low because the period becomes long.

Furthermore, in the above equation (1), in order to obtain the power factor angle, the O-cross point of the current waveform is also required, and in addition, it is also necessary to obtain the electrical angle between the zero-cross points of the voltage and current.

This is a problem that always accompanies a method that includes an operation for calculating an average value, even if the principle of detecting the generated torque is different.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a generated torque detection device for an induction motor that can easily detect instantaneous generated torque.

[Structure of the invention]

(Means for Solving the Problems) The present invention provides voltage detection means and current detection means for detecting the input voltage and input current of an induction motor and outputting respective instantaneous values or signals proportional to the instantaneous values; Determine the peak value and effective value of the input terminal and input current from the output of the detection means, and determine the phase difference between the input voltage and input current from the peak value and the instantaneous value or a signal proportional to this instantaneous value. , calculating the input power of the induction motor from the input current, each effective value of the input current, and the phase difference, and dividing this input power by the rotational speed of the induction motor to calculate the instantaneous generated torque of the induction motor. It is equipped with means.

(Function) If the input phase voltage effective value V1 of the induction motor, the input terminal effective value I, and the instantaneous values of the power factor angle θ, − as seen at the input end, are obtained, then the generated torque Tc can be obtained according to equation (2). There is.

In this case, the instantaneous effective value is determined as follows.

Although the concept shown here can also be applied to multi-phase balanced AC waveforms, a three-phase balanced AC waveform will be particularly described.

First, assuming that the peak value is 11 and the electrical angular velocity is ω, the three-phase current waveforms i3, i5, and ie are expressed as in the following equations.

i 111slnω conflict t a e tb−i −5ln (ω, −t+ 2π/3)i
-i -51n (ω·t+4π/3)Ce If each of these times is detected, the peak value i is obtained by the following equation.

(3) Equation (3) shows that the peak value can be found from the instantaneous value of each sum waveform. Therefore, the instantaneous effective current value!
can be calculated using the following formula.

1--i
(4) T In the same way, the instantaneous effective voltage value V can also be determined by the following equation.

On the other hand, as shown in FIG. 8, the instantaneous value of the a-phase current at a certain time t' is i', and the instantaneous value of the a-phase voltage is V'.
Then, each phase angle θ1 of these currents and voltages is θ1. and θ1. can be obtained from the following equation.

The relationship in equation (6) above applies when 0≦θ1a≦π12, and covers the entire range of phase angles, that is, 0≦01. In the range of ≦2π, it is necessary to judge from the polarity of i and the magnitude of ibl io which of the four sections 11■, ■, ■ shown in FIG. 9 it belongs to, and then correct the value.

That is, if 11 ≧0 and lb≦lc, then 0≦θl, ≦π121
1i ≧0 and tb>1. Then π/2<θI, ≦π
If m i <0 and ib>10, π and θ1a<3
If π12IVi<O and lb≦1 c, then 3π12≦θ
The interval may be determined by la' 2π and corrected as follows.

a) In case of I: θIa - Right side of equation (8) b) In case of n: θia - Right side of equation (6) + π12c) II
In case of I: θ1a = right side of equation (8) + πd) In case of IV: θia = right side of equation (8) + 3π12 Also, above (7)
The relationship in the equation is for 0≦θVa≦π/2, and in the entire range of phase angles, that is, in the range 0≦θ≦2π, the polarity of V and va
From the size of aV b s V o, four sections 1. It is only necessary to determine whether it belongs to II, ■, or ■, and then modify its value.

That is, if Iv≧0 and vb≦Vc, then 0≦θ1. ≦yr1
211v ≧0 and Vb > ve, then π/2<
If θva≦πm v <o and Vb>vc, π minus θ, <3yr/2IVv<0 and vb≦v0, then 8yr/2≦θ, a≦2π, determine the interval, and correct as follows. do it.

a) For I: θ - Right side of equation (7) a b) For n: θ - Right side of equation (7) + π12a c) For III: θ - Right side of equation (7) 1πa d) For IV 20 −(7) formula right base+3π12a Thereby, the power factor angle θ, F can be determined by the following formula.

θ, F-~, -θ1a...(8)
Next, the power loss Ploss at the resistances r 1 and r 2 is given by the following equation.

P −3(r + r )I cos θp
p"' (9) loss 1 2 Note that this power loss Ploss may be calculated by the following equation using the peak value i found by equation (3).

In this way, all the quantities necessary for calculating equation (2) are obtained, and as a result, the torque T6 generated by the induction motor is obtained as an instantaneous value.

In accordance with this principle, the present invention first detects the respective instantaneous values of the input voltage and input current of the induction motor, then determines the peak values of the voltage and current from these detected values, and calculates the peak values of these currents. Find the effective value of and voltage and the phase difference between both waveforms, that is, the power factor angle. Find the input power from this effective value and power factor angle. Divide this by the rotational speed to calculate the instantaneous torque generated by the motor. It is something to seek.

(Embodiment) FIG. 1 is a schematic configuration diagram of an embodiment of the present invention. A voltage fundamental wave detection circuit 4 and a current fundamental wave detection circuit 5 are provided between the induction motor 2 and the induction motor 3, each detection signal of these detectors, and the detection of the speed detector 6 coupled to the induction motor 3. The generated torque calculation circuit 7 calculates the generated torque by inputting the signal.

FIG. 2 is a block diagram showing the detailed configuration of the generated torque calculation circuit 7. As shown in FIG. In the figure, multipliers 711 to 711 each square the output of the voltage fundamental wave detection circuit 4 described above.
713, a logic circuit 740 that determines which of the three-phase AC sections I, II, ■, ■ belongs to based on the output of the voltage fundamental wave detection circuit 4, and a current fundamental wave detection circuit 5. Multipliers 714 to 7 that square the outputs respectively
16, and section 1 of the three-phase alternating current based on the output of this current fundamental wave detection circuit 5. It also includes a logic circuit 741 that determines whether it belongs to II, ■, or ■. Among these, the multipliers 711 to 713 have an addition coefficient squarer 717 that performs summation, coefficient multiplication, and square root calculation, and the multipliers 714 to 716 have an addition coefficient squarer 71 that also performs summation, coefficient multiplication, and square root calculation.
8 are connected to each other. On the other hand, the three-phase detection values of the voltage fundamental wave detection circuit 4 are sent to the absolute value generator 7111, and the three-phase detection values of the current fundamental wave detection circuit 5 are sent to the absolute value generator 7114.
are added to each, and the absolute value of each is calculated. Then, there is a divider 719 which has the output of the absolute value generator 7111 as one input and the output of the addition coefficient squarer 717 as the other input, the output of the absolute value generator 7114 as one input, and the output of the addition coefficient squarer 718 as the other input. A coefficient unit 723 which inputs the output of the addition coefficient squarer 717 to obtain the effective value, and a coefficient unit 7 which inputs the output of the addition coefficient squarer 718 to obtain the effective value.
It is equipped with 24.

Next, inverse sine function units 721 and 722 are connected to the dividers 719 and 720, respectively. And logic circuit 7
40 as one input, and the output of the inverse sine function unit 721 as the other input; and an adder 726, which has the output of the logic circuit 741 as one input, and the output of the inverse sine function unit 721 as the other input. We are prepared. Furthermore, the adder 72
a subtracter 727 that subtracts the output of the adder 726 from the output of 5;
is provided, and its output is applied to a cosine function unit 728. In addition, the output of the coefficient unit 723 and the coefficient unit 72
4, and its output is added to a coefficient unit 730.

Next, the output of the cosine function unit 728 and the output of the coefficient unit 730 are multiplied by the multiplier 731, and the multiplication output is
It is added as one input of 36. Also, cosine function unit 7
28 is squared by a multiplier 732, the output of the addition coefficient squarer 718 is squared by a multiplier 733, these two squared outputs are multiplied by a multiplier 734, and then the coefficient multiplier 735
is multiplied by a coefficient and added as the other input of the subtracter 736. The output of the subtracter 736 is divided by the detection signal of the speed detector 6 by a divider 737.

The operation of this embodiment configured as described above will be explained below.

Multipliers 711 to 716 square the instantaneous values of voltage and current of each phase, respectively. The squared values obtained here are summed by the addition coefficient squarer 717 and 718 for each voltage and current, respectively.
The coefficient is multiplied by the square root. The coefficients here are 273 for both voltage and current. Addition coefficient squarer squarers 717 and 718 output peak values of voltage and current. Dividers 711 and 714 divide the absolute values of voltage and current phases obtained by absolute value generators 7111 and 7141 by these peak values,
By inputting the results to the arc sine function units 721 and 722, the angles θ1 and θ of the above equations (6) and (7),
is obtained.

On the other hand, the output of the addition coefficient squarer 717 and 718 is
23 and 724, each is multiplied by l/42 to obtain an effective value. In addition, the logic circuits 740 and 741 determine which of the four intervals (■, ■, ■, ■) the current moment belongs to, divided by 0 to 2π, and output the correction values shown in a) to d). . Therefore, the adder 725 is the inverse sine function unit 721
The adder 726 adds the output of the arc sine function generator 722 and the correction value of the logic circuit 741 to output the corrected phase angle θ. outputs the phase angle θ1.

Next, when the subtractor 727 subtracts the phase angle ■ θ from the phase angle θ 2 and outputs the power factor angle θ, P, the cosine quantity calculator 728 calculates the power factor cos θpp. Also, the coefficient unit 72
The effective values of the voltage and current obtained in steps 3 and 724 are multiplied by a multiplier 729, and the output thereof is further multiplied by 3 by a coefficient multiplier 730. Subsequently, in the multiplier 731, the coefficient unit 730
The output of the cosine function unit 728 is multiplied by the output of the cosine function unit 728 to obtain the human power PIn.

On the other hand, the output of the cosine function unit 728 and the addition coefficient squarer unit 718
Multipliers 732 and 733 square the outputs of
Power loss Ploss based on equation (10) is calculated by multiplying by /2 (rl+r2).

Next, a subtracter 736 subtracts the power loss Ploss from the input power P1n, and a divider 737 divides the obtained difference by the rotational speed to obtain the instantaneous value of the torque generated by the induction motor.

Note that, if harmonics are included in the voltage and current waveforms, the calculation in the above equation is performed after removing the harmonic branches using a low-pass filter.

Furthermore, in this example, for ease of understanding, (
1) The configuration corresponds to formulas (1) to (lO), but in particular,
It goes without saying that the circuit can be simplified by grouping the coefficients of each part as appropriate.

FIG. 3 is a schematic configuration diagram of another embodiment of the present invention, which is particularly applied to a system in which an induction motor is driven by a voltage source inverter. Here, inverter 2 shown in FIG.
Instead, a voltage source 2a is used and is controlled by the ignition circuit 8a, while based on the output of the current fundamental wave detection circuit 5, the detection signal of the speed detector 6, and the control signal of the ignition circuit 8a. Therefore, the generated torque calculation circuit 7a is connected to the induction motor 3.
This is to calculate the generated torque.

In the ignition control of the voltage source inverter 2a, since the magnitude and frequency of the voltage are given as command values, the instantaneous value, peak value, and effective value of the voltage can be easily obtained from the command value without using the calculation using the instantaneous detection value described above. can be obtained. Further, in the ignition control circuit 8a, in order to obtain the ignition signal of each phase, a reference signal of the output voltage waveform of each phase is generated from the magnitude and frequency of the voltage given as a command value within the circuit. This signal has a waveform similar in principle to the voltage waveform of each phase obtained by the voltage detector 4 of the above embodiment. Strictly speaking, harmonics caused by modulation in the inverter, control delay, detection delay,
This is an ideal waveform with no phase rotation in the filter or waveform distortion due to floating elements.

This waveform can be used in place of the voltage detection value.

FIG. 4 is a block diagram showing a detailed configuration of the generated torque calculation circuit 7a taking this into consideration, and the same reference numerals as in FIG. 2 indicate the same elements. Here, the reference signal of the output voltage waveform of each phase generated by the ignition control circuit 8a is given to the logic circuit 740 to determine which of the sections 11■, 2, and 11 belongs to, and a) While outputting the correction values shown in ~d), the a-phase component of the reference signal of the output voltage waveform is given to the absolute value circuit 711 to calculate its absolute value. Further, the command value of the magnitude of the voltage generated by the ignition control circuit 8a is given to the coefficient unit 751 to obtain the peak value V 1 of the voltage, and the command value is given to the coefficient unit 752 to obtain the effective value V 2 of the voltage. The wave height value V is given to a divider 719, and the effective value V is given to a multiplier 729, respectively.

According to this configuration, the voltage detector 4 is not required, and at the same time, the configuration of the generated torque calculation circuit is simplified.

ff! FIG. 5 is a schematic configuration diagram of another embodiment of the present invention, which is particularly applied to a system in which an induction motor is driven by a current source inverter. Here, a current source inverter 2b is used instead of the inverter 2 shown in FIG. 1, and this is controlled by an ignition circuit 8b. Based on the control signal of the arc control circuit 8b, the generated torque calculation circuit 7b
is used to calculate the torque generated by the induction motor 3.

In the ignition control of the current source inverter 2b, the magnitude and frequency of the current are given as command values, so the instantaneous value, peak value, and effective value of the current can be easily obtained from the command value without having to calculate using the instantaneous detection value described above. can be obtained. Further, the ignition control circuit 8b generates a reference signal for the output current waveform of each phase from the magnitude and frequency of the current given as a command value within the circuit in order to obtain the ignition signal of each phase. This signal has a waveform similar in principle to the current waveform of each phase obtained by the current detector 5 of the embodiment shown in FIG. Strictly speaking, harmonics caused by modulation in the inverter, control delay,
This is an ideal waveform with no detection delay, phase rotation in filters, or waveform distortion due to floating elements. This waveform can be used in place of the current detection value.

FIG. 6 is a block diagram showing a detailed configuration of the generated torque calculating circuit 7b taking this into consideration, and the same reference numerals as in FIG. 2 indicate the same elements. Here, the reference signal of the output current waveform of each phase generated by the ignition control circuit 8b is given to the logic circuit 741 to determine which of the sections I, II, ■, ■ belongs to, and a While outputting the correction values shown in ) to d), the a-phase component of the reference signal of the output current waveform is supplied to the absolute value circuit 7114 to calculate the absolute value thereof. In addition, the ignition control circuit 8
The command value of the magnitude of the current generated in b is given to the coefficient unit 761 to obtain the peak value i of the voltage, and the command value is given to the coefficient unit 762 to obtain the effective value I of the current. 720 and a multiplier 733, and the effective value {circle around (2)} is applied to a multiplier 729, respectively.

According to this configuration, the current detector 5 is not required, and at the same time, the configuration of the generated torque calculation circuit is simplified.

Although the present invention has been described above with reference to three embodiments, the present invention is not limited thereto. For example, a computer may be used as the generated torque calculation circuit, and the above functions may be provided by software.

Further, in the above embodiment, the voltage-related signal is obtained from the phase voltage, but even if it is obtained from the line voltage, the same operation will be performed if the correspondence between the phase voltage and the line voltage is considered. can be set.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, the instantaneous value of the torque generated by the induction motor can be detected using the instantaneous values of the voltage and current of the induction motor.

FIG. 7 is a block diagram showing the configuration, FIG. 7 is an equivalent circuit diagram of a general induction motor, and FIGS. 8 and 9 are waveform diagrams for explaining the present invention in detail.

1...DC power supply, 2, 2a, 2b...inverter,
3... Squirrel cage induction motor, 4... Voltage fundamental wave detection circuit, 5... Current fundamental wave detection circuit, 6... Speed detector, 7.7a, 7b... Generated torque calculation circuit, 8a, 8
b...Ignition control circuit.

[Brief explanation of the drawing]

Claims (1)

[Claims] Voltage detecting means and current detecting means detect the input voltage and input current of the induction motor and output respective instantaneous values or signals proportional to the instantaneous values, and detect the input voltage and input current from the outputs of these detecting means. A peak value and an effective value are determined, a phase difference between the input voltage and input current is determined from the peak value and the instantaneous value, or a signal proportional to this instantaneous value, and each effective value of the input voltage and input current is determined from the phase difference between the input voltage and the input current. An induction motor characterized by comprising: calculating means for determining the input power of the induction motor from the phase difference and dividing this input power by the rotational speed of the induction motor to determine the instantaneous generated torque of the induction motor. Generated torque detection device.